The semiconductor industry's continuing drive toward integrated circuits with ever decreasing geometries, coupled with its pervasive use of highly reflective materials, such as polysilicon, aluminum, and metal silicides, has led to increased photolithographic patterning problems. Unwanted reflections from these underlying materials during the photoresist patterning process often cause the resulting photoresist patterns to be distorted. This problem is further compounded when photolithographic imaging tools utilizing deep ultraviolet (DUV) exposure wavelengths (approximately 248 nanometers (nm)) are used to generate the photoresist patterns. Although shorter imaging wavelengths bring improved resolution by minimizing diffraction limitations, the resulting patterns generated in the photoresist are easily compromised by the effects of uncontrolled reflections from underlying materials due to the increased optical metallic nature of underlying reflective materials at these shorter wavelengths. Moreover, photoresist patterns are particularly degraded in areas where the topology of the underlying reflective material changes. In stepped areas of semiconductor devices, reflection intensity from underlying materials is often enhanced and results in "reflective notching" or a locally distorted photoresist pattern near the stepped areas. Therefore, the formation of submicron photoresist patterns over semiconductor substrates using DUV lithography is difficult to achieve, and as a result, fabrication of advanced integrated circuits with submicron geometries is limited. Moreover, many known anti-reflective coating materials used in semiconductor manufacturing are not suitable for use with DUV lithography. For example, titanium nitride is increasingly metallic as exposure wavelength is reduced to the DUV range of 248 nm, meaning titanium nitride has high reflectivity for DUV radiation and is not an effective anti-reflective coating for DUV. While silicon-rich silicon nitride has been suggested for use as an anti-reflective coating with DUV, it cannot be used on aluminum because process temperatures for forming the silicon-rich silicon nitride are too high for back-end processing.
Accordingly, a need exists for a method that forms submicron integrated circuit patterns in a photoresist layer which overlies the varying topography and highly reflective materials found on semiconductor substrates. Particularly useful would be a method which compliments the use of DUV lithography.